Data input devices are commonly used in conjunction with electronic appliances to feed them with various kinds of data, including e.g. control data influencing directly or indirectly the behavior of the appliance, data that are processed by the appliance and/or simply stored.
It is known to construct data input devices based upon film-type pressure sensors. A film-type pressure sensor comprises two carrier films, which are arranged at a certain distance from one another by means of a spacer. The spacer is provided with at least one opening that defines an active zone of the sensor, in which the two carrier films face one another. Inside this active zone, at least two electrodes are arranged in such a way on the carrier films, that electrical contact is established between the electrodes when the two carrier films are pressed together under the action of a compressive force acting on the sensor in the active zone.
Depending on the application of such a pressure sensor, a layer of semiconducting material may be disposed between the electrodes, so that the sensor shows a gradual pressure sensitive behavior, that is to say its resistance varies gradually or even continuously as a function of the force applied. The layer of semiconducting material may comprise a material whose internal electrical resistance varies as a function of compression or of deformation of the layer or a material whose surface structure confers to the layer a surface resistance that is reduced following an increase in the number of points of contact with a conducting surface of an electrode, against which the layer of semiconducting material is pressed under the action of the compressive force.
WO 2004/049364 relates to a data input device comprising several keys arranged in at least two rows. A unidirectional position detector of film-type construction is associated with each row of keys Each unidirectional position sensor enables the detection of the actuated key along the direction of the unidirectional position detector. The unidirectional position sensors are interconnected in such a way that a control circuit can detect in which row a key has been actuated.
A different kind of sensors is based upon capacitive sensing. U.S. Pat. No. 3,896,425 discloses an electrical proximity detector that senses the changes in the contents of a defined sensitive volume. The detector comprises an antenna that is driven by an oscillator and that emits an electric field into the sensitive volume. A person or an object intruding into the sensitive volume causes a change of the electric field of the antenna, which is detected by the detector. To shape the electric field of the antenna the detector comprises a first shield, driven by the oscillator with a signal of same amplitude and phase as the signal of the antenna, and a second, grounded shield.
Other sensors based on electric field or “capacitive” sensing have been proposed by J. Smith et al. in “Electric Field Sensing for Graphical Interfaces”, IEEE Computer Graphics and Applications, Issue May/June 1998, 54-60, as a human-computer interface. The interfaces are based upon an array of electrodes to detect the gestures of a user.
The above-mentioned documents are herewith included herein by reference.